Introduction to Seam Pete Muir JBoss, a division of Red Hat
Road Map Background Seam concepts Seam with Wicket (at the BOF) Seam Extras 2
Advantages of JSF/JPA over Struts/EJB 2 Fewer, finer grained artifacts No DTOs required Clean MVC Less noise No Struts/EJB 2.x boilerplate code No direct calls to HttpSession or HttpRequest Simple ORM Even simpler than the Hibernate API! 3
Advantages of JSF/JPA over Struts/EJB 2 JSF is flexible and extensible Custom UI widget suites (open source) Good AJAX support JPA Powerful object/relational mapping, far beyond EJB 2.x CMP entity beans All components are POJO so easily testable with TestNG or JUnit 4
But, still some problems JSF Backing bean couples layers and is just noise Hard to refactor all the XML and String outcomes No support for the business layer Validation breaks DRY XML is too verbose How do we write our business layer EJB3? - can t be used directly by JSF EJB3? - no concept of scopes 5
And, some other stuff to solve! Workflow Ad-hoc back buttoning not suppored No stateful navigation Long running business processes? Multi-tab/window support is not built in All operations happen in the session - leakage No support for a conversation context Memory leak - objects don t get cleaned up quickly 6
Simple JSF with Seam Reference the entities directly! <h:form> Item: <h:outputtext value="#{itemeditor.id} /> Name: <h:inputtext value="#{itemeditor.item.name}"> <f:validatelength maximum="255" /> </h:inputtext> Price (EUR): <h:inputtext value="#{itemeditor.item.price}"/> <f:convertnumber type="currency" pattern="$###.##" /> </h:inputtext> <h:messages /> <h:commandbutton value="save" action="#{itemeditor.save}" /> </h:form> 7
Adding Seam A conversation scoped Seam component @Name("itemEditor") @Scope(CONVERSATION) public class EditItemBean implements EditItem { @In EntityManager entitymanager; Long id; Item item; // getter and setter pairs @Begin public String find(long id) { item = entitymanager.find(item.class, id); } return item == null? "notfound" : "success"; Begin and End a conversation - state is maintained over multiple requests between these methods @End public String save(item item) { } item = entitymanager.merge(item); return "success"; 8
Road Map Background Seam concepts Seam with Wicket Seam Extras 9
Contextual variables Contexts available in Seam Event Page Conversation Session Business Process Application 10
JSF lifecycle - quick review RESTORE VIEW: Restore the tree of UI components APPLY REQUEST VALUES: Synchronize request parameters with UI components PROCESS VALIDATIONS: Validate state of UI components UPDATE MODEL: Synchronize UI components with bound backing bean properties INVOKE APPLICATION: Notify action listeners, call action methods RENDER RESPONSE: Render a new tree of UI components 11
Application lifecycle Seam provides hierarchical, stateful contexts BUSINESS PROCESS APPLICATION SESSION SESSION CONVERSATION CONVERSATION EVENT EVENT EVENT PAGE INVOKE APPLICATION RENDER RESPONSE INVOKE APPLICATION 12
How is state stored? Depends on the context: Conversation context Segmented HttpSession - times out if not used Page context Stored in the component tree of the JSF view (page) Can be stored in HttpSession or serialized to client Business Process context 13
Bijection Seam provides hierarchical, stateful contexts (Dependency) Injection fine for stateless applications BUT stateful applications need bidirectional wiring. Think about aliasing a stateful object into a context @Name("passwordChanger") public class PasswordChanger { @In EntityManager entitymanager; @In @Out User currentuser; } public void changepassword() { } entitymanager.merge(currentuser); Bijection: before the method call, inject the current user; after the method call, save it back into the context. 14
JPA Persistence Context What is the Persistence Context? a HashMap of all the objects I ve loaded and stored holds (at most) one in-memory object for each database row while the PC is active a natural first-level cache can do dirty checking of objects and write SQL as late as possible (automatic or manual flushing) The Persistence Context has a flexible scope default: same scope as the system transaction (JTA) extended: the PC is bound to a stateful session bean 15
Which PC scope to use? Transaction scoped & detached objects LazyInitializationException NonUniqueObjectException Less opportunity for caching An extended persistence context of a SFSB is not available during view rendering (LIE again) very complicated propagation rules No concept of a conversation 16
Seam managed persistence and transactions Seam managed PC is conversation scoped Remains active through conversation, Inject using @In Allows use of manual flush mode CONVERSATION EVENT EVENT RESTORE VIEW APPLY REQUEST VALUES PROCESS VALIDATIONS UPDATE MODEL INVOKE APPLICATION RENDER RESPONSE PERSISTENCE CONTEXT FLUSH SYSTEM TRANSACTION 17
Navigation Stateful Pageflow powered by jbpm engine (graphical editor) Back button normally disabled Stateless Through JSF or pages.xml pages.xml is very powerful compared to JSF navigation rules (outcomes, application state, raise events on navigation) 18
Workflow - Business Process Management What is it? Very long running (multiple days) Lots of users (tasks can be assigned) Can contain many tasks A task is completed by one user Often a conversation 19
Model based validation Validate in the user interface? Yes, need to report validation errors back to the user on the correct field BUT normally need to enforce same constraints at the persistence layer and the database public @Entity class Item { @Id @GeneratedValue Long id; String name; @Length(min=3, max=1000, message="must be between 3 and 1000 characters") String description; 20
Hibernate Validator Many built-in validators: Max, Min, Length, Range, Size, Email, Future, Past, Pattern, Email, CreditCard,... Easy (very) to write custom validators Validation and message/error display with Seam UI components for JSF Works with every JPA provider, if used with Hibernate it generates SQL DDL constraints you can use in your database schema Standardization effort under way - JSR 303 21
Road Map Background Seam concepts Seam with Wicket Seam Extras 22
Seam Application Framework <components> <fwk:entity-home name="userhome" entity-class="user" /> </components> <h:form> <h:inputtext value="#{userhome.instance.name}" /> <h:inputsecret value="#{userhome.instance.password}" /> <h:commandbutton action="#{userhome.update}" /> <h:messages /> </h:form> 23
Contextual Events @Name("hotelBooking") public class HotelBooking { } @End public void confirmroomchoice() { booking.setroom(chosenroom); } Events.instance().raiseEvent("roomChosen"); public @Name("RoomList") class RoomList { @Out List<Room> availablerooms; } @Observer("roomChosen") public void refresh() { } availablerooms = entitymanager.createquery("select..."); 24
And more Security Email PDF Remoting Asynchronicity (Java SE, EJB3 or Quartz) Google your app using Hibernate Search Integration and Unit Testing JSF components (deep integration into JPA) Components in groovy Webservices > 25 examples Portal support 25
Want to learn more? Security SSO Identity Management GWT Wicket? Flex? Web Beans! http://www.seamframework.org 26
Go get it! Security SSO Seam Identity in Management JBoss Enterprise Application Platform 4.2 - GWTsupported product with Seam 1.2 Wicket? Seam 2.0.1.GA - community release of Seam2 Flex? Web Seam Beans! 2.1.0.A1 - preview release of Seam 2.1 with Wicket and Portal support 27
The future of Seam? Security SSO Identity Web Beans!! Management GWT Wicket? First class support for other other containers (e.g. Flex? Websphere) Web Beans! Friendly URLs Identity Management SSO for security Flex support (talk at JBoss World!) Deeper integration with JBoss Portal (inter-portlet communication) 28
Q&A 29
More Seam at JBoss World Gavin is talking about Web Beans at 1:40pm on Friday Seam, Tools and Web Beans BOF tonight at 8pm 2 (!) Seam Case Studies on Friday at 9am Agile development on Friday at 1:40pm on Friday 30